Nucleotides related substances

Bioassays of related substances can be quite similar in design. Specific growth factors, for example, stimulate the accelerated growth of specific animal cell lines. Relevant bioassays can be undertaken by incubation of the growth-factor-containing sample with a culture of the relevant sensitive cells and radiolabelled nucleotide precursors. After an appropriate time period, the level of radioactivity incorporated into the DNA of the cells is measured. This is a measure of the bioactivity of the growth factor. 

Besides being fundamental constituents of proteins they are the parent substances from which powerful hormones are derived, for example, adrenaline (epinephrine), noradrenaline (norepinephrine), thyroxine and related substances, 5-hydroxytryptamine (enteramine, serotonin), and the plant hormone indoleacetic acid. Tryptophan is also the precursor of the B vitamin nicotinic acid and hence of part of the important pyridine nucleotides. All three aromatic amino acids are potential precursors of other substances having powerful physiological activity, for example, many of the alkaloids. Errors in the metabolism of the aromatic amino acids in man can give rise to sometimes serious, but fortunately comparatively rare, disorders such as alkaptonuria and phenylketonuria. The numerous metabolic pathways involved in aromatic amino acid metabolism therefore make an important as well as an interesting study. 

To analyze the spectral tuning of dCRNs, food extracts or mixtures of chemicals mimicking such extracts have been used as search stimuli and this limits our knowledge about stimulatory chemicals for crustacean dCRNs to mainly food-related substances. The chemicals most widely tested and found to be stimulatory are L-amino acids followed by ammonium chloride, betaine, nucleotides, amines, sugars, pyridines, organic acids, and small peptides. Only rarely, other chemicals, including the putative pheromone ecdysone (Spencer and Case 1984), were tested... 

The addition of riboflavin to the system repeatedly caused a small but significant synthesis of cyanocobalamin. More efficient shunting of the synthesis toward cyanocobalamin took place when parts of the riboflavin molecule and related substances were added, e.g. l-amino-3,4-di-methyl-6-D-ribitylaminobenzene l,2-dimethyl-4,5-diaminobenzene and 5,6-dimethylbenzimidazole. These findings seem consistent with the view of Woolley (1951) that the metabolic paths of the two vitamins are closely interconnected. The activity of riboflavin itself in promoting the synthesis of cyanocobalamin need not of course imply that the vitamin is actually broken down to provide a precursor of cyanocobalamin nucleotide. It could equally well be that a common precursor of riboflavin and cyanocobalamin nucleotide is normally available in limiting amounts and is used preferentially in the synthesis of riboflavin. The provision of preformed riboflavin might then spare this precursor for the synthesis of cyanocobalamin. 

Bumstock, G, Campbell, G, Satchell, D and Smythe, A (1970) Evidence that adenosine triphosphate or a related nucleotide is the transmitter substance released by non-adrenergic inhibitory nerves in the gut. Brit. J. Pharmacol. 40 668-688. 

The substances which help an enzyme work are called activators or coenzymes frequently they are metal ions or such substances as nucleotides. Sometimes a coenzyme is bound so firmly to the enzyme surface that it is not even removed by dialysis in this case it is described as a prosthetic group, But activators, coenzymes, and prosthetic groups all fulfil the same function of tailoring the enzyme to fit the substrate. In Figure 14 we have made a schematic drawing of the relations between enzyme, cofactors, and substrate for a hypothetical enzyme. 

Many of the enzymes that display such behaviour also respond to heterotropic effectors [32] i.e. substances that are not obviously related to the substrates an example is the regulation of aspartate transcarbamylase [31] by CTP (inhibitor) and ATP (activator), neither nucleotide being a substrate for this enzyme. 

Purines, Fischer investigated uric add and related purines during the period 1881-1914 in 1914 he achieved the first synthesis of a nucleotide. He investigated the entire series of purines, estabfished their structure, and synthesized the parent substance (purine) and about 130 derivatives. 

It is clear that no genetic system could have been based on these isomeric nucleotides, in which one does not see the association of two strands to transfer and utilize the genetic coding, only three strand association of a special sort. Such studies— related to those by Eschenmoser [7] in which ribose was substituted by other sugars— give us insight into the special chemical properties of natural substances such as DNA that allow them to perform their biological functions. 

As mentioned above, immobilized cells are studied mainly for practical reasons, since they show a number of economic advantages over the use of growing cells or cell suspensions. Production of organic acids is one of the prospective applications of immobilized cells. Another one is related to the release of nitrogenous bases and some nucleosides by immobilized cells. In nitrogen-starved immobilized cells the levels of all metabolites (first of all, nucleotides) are reduced (Leps and Ensign, 1979). It was shown (Ikonnikov et al., 1982) that immobilized cells of propionic acid bacteria, incubated periodically in nitrogen-free medium, released substances of protein and nucleic acid nature, whose quantity decreased with the time of incubation in... 

---